Method of preparing building materials

ABSTRACT

A method of making a building material by activation of latently hydraulic finely ground granulated basic blast-furnace slag to form a direct acting hydraulic binder. The slag is mixed with water, sand and ballast material as well as with a combination of acidic and basic components. The acidic components consist of phosphates, optionally in combination with strongly acting sulfates, and the basic components consist of oxides or other compounds of earth metals, optionally in combination with zinc. Thereby, a concrete having great mechanical strength and high chemical resistance is obtained.

This is a request for a filing under the file wrapper continuingapplication Procedure, 37 CFR 162, for a continuation of prior completeapplication Ser. No. 07/569,227, filed on Aug. 17, 1990 which is acontinuation application of Ser. No. 07/344,208 filed Apr. 27, 1989 (nowabandoned) which is a continuation-in-part application of Ser. No.07/071/794 filed June 11, 1987 (now abandoned).

Portland cement is generally considered as the best hydraulic binder,which only by addition of water and aggregate hardens to form arock-like material (concrete) within a few hours to obtain finally itsultimate strength within about one month. The effect is due mainly tochemical reactions between basic lime and silicic acid. Analysis ofPortland cement shows about 64% CaO, 20 % Si02, 2.5 % MgO, 6 % A1203 3.5% Fe203 +FeO, 2% K20 +Na20, 1.5% SO₃. A disadvantage of cement is thatnot all lime is bound in the concrete and that a consistently appearingexcess of unstable hydrate of lime, which is formed towards the end ofthe hardening process, is relatively easily leached out by the action ofwater and carbon dioxide in the air, involving a danger of detrimentalcarbonization. Furthermore, the chemical resistance to acidic and basicattack is very limited.

Example: Destruction of concrete surfaces on roads by road salts or ofconcrete bridges by sea-water. Risk of rust attack on steelreinforcement and great difficulties with glass fibre reinforcement.

To avoid the sometimes disturbing weakness of Portland cement, materialshaving a similar composition but with an enhancement of the componentsimproving both the physical and the chemical resistance have long beensought. It was natural to experiment with finely ground granulated basicblast-furnace slag as it has a high percentage of highly resistantsubstances. The analysis is as follows, varying with the source: about30 to 40 CaO, 35 to 40% SiO₂, 7 to 10% MgO, 10 to 20 % Al₂ O₃, 0.5 to 2% Fe₂ O₃ +FeO, 1 to 2 % K₂ O +Na₂ O, 0.5 to 3 % SO₃. Compared toPortland cement, the lime content is only about one-half, but SiO₂ andAl₂ O₃ is about double, and MgO almost four times higher. Thesesubstances, however, impart to silicates the highest mechanical andchemical resistance, i.e. increased compressive and tensile strength andresistance to chemical action.

Blast furnace slag is obtained largely as a useless residual product inthe manufacture of iron and steel and is present internationally inhundreds of millions of tons. "Granulated" generally means "subdivided",but in connection with slag it is commonly meant that the slag in astill red-hot state has been subjected to rapid cooling with water orwith a combination of cold water and cold air, whereby the slag becomesvitreous and amorphous. In spite of the favorable chemical composition,the finely ground granular blast-furnace slag is only "latently"hydraulic, i.e. it does not bind automatically after admixture withwater. The reason is that a dense gel rich in silicic acid is formedsaid gel enclosing the slag grains and preventing hydration. A conditionfor accomplishing activation is that this gel is broken. Thus,activators have a double task; they must first break down the gel andthen react with the slag itself. However, the gel formation also has apositive effect, since the gel pores are uniformly distributed, wherebya better resistance to frost is obtained than with capillary pores inPortland cement concrete.

Already toward the end of the nineteenth century attempts to activateblast-furnace slag were made. The oldest patent goes back to 1892(Passow), wherein a mixture of slag with Portland cement is recommendedand wherein the free lime in the form Ca(OH)₂ formed in the final stageof hydration functions as an activator. Thereby, the reaction with slagoccurs late and gives rise to a slow development of strength. Also therisk of shrinkage in cooling is rather great. This is the reason why inmany countries the so-called slag cement is hardly used at present.

In addition to lime, prior known activators (see H. Khl, Zement-Chemie,Berlin 1951) are alkalies and sulfates. Hitherto, it was thought thatactivation with alkalies resulted in the highest strength values, but itresulted in a number of disadvantages. The long-term strength is notsatisfactory, and there are great risks of shrinkage, salt depositionmicrocracks, and carbonatization. Setting occurs too quickly, in 10 to30 minutes, wherefore casting in a building site is not possible. Use islimited to the manufacture of prefabricated or precast units. Activationby alkalies also has the disadvantage that strong caustic NaOH isformed. Activation by sulfates has the disadvantage of an inferiorshort-term strength and a risk of swelling. For all these known methodsit is also difficult to control the rate of setting which is either toorapid or too slow.

The setting time has to be controlled according to the circumstances.There are different well-known actions which can be applied if a shortsetting time is required, for example, a finer grinding of thecomponents and high temperature of about 50-80° C. during the first dayof setting. Activation by alkalies is the most widely used activationmethod today but this method is already too rapid, therefore, the aboveactions for controlling the setting time cannot be applied. Nor arethese actions suitable for the prior known mixture of slag and Portlandcement, because the activator Ca(OH)₂ is formed in the final step ofhydration after several hours.

A retardation of the setting time is possible by sulfates or Plaster ofParis. In the claimed method, an addition of less than 3 % by weight issuitable, but the prior known activation by alkalies requires a muchlarger amount resulting in damaging expansion of the produced concrete.

A much more reliable activation technique is obtained by the combinationof acidic and basic components wherein the acidic component consistspreferably of phosphates, optionally in combination with strongly actingsulfates, and the basic components are earth metal oxides and optionallyalso zinc oxide, and addition of water resulting in a hydraulicreaction. Earth metal oxides are magnesium oxide, calcium oxide,strontium oxide, barium oxide, aluminum oxide, beryllium oxide, galliumoxide, indium oxide, thallium oxide, titanium oxide, and zirconium oxideand the so-called rare earth metal oxide. Most effective is magnesiumoxide, which has the best improving effect on silicates, as it enhancesthe compression and tensile strengths and the elasticity, reducesshrinkage and results in a non hygroscopic product. Normally MgO can beincorporated in silicates only by melting at a high temperature.Together with phosphates, optionally in combination with sulfates, ahydraulically acting reaction is achieved with finely ground granulatedbasic blast-furnace slag. The best action is obtained with calcinedmagnesia (fired at about 1750.C., whereby all water and carbon dioxidehave been driven off). Less suitable are MgO containing minerals, e.g.dolomite, which act more as fillers. Furthermore dolomite, MgCa(CO₃)₂,contains calcium, which reacts directly with phosphate forming apatite,as generally known. However apatite is not a binder. The earth metaloxides are suitably included in an amount of 0.3 to 3 % by weight, basedon the dry concrete (i.e. slag +sand +aggregate) or 2 to 20 % by weightbased on the slag.

The acidic components are suitably included in an amount of 0.3 to 6 %by weight, based on the dry concrete, or 2 to 40 % by weight based onthe slag.

The building material formed according to the invention has a lowcalcium content compared to building materials formed, for example, withPortland cement, and no unbound lime. Compared to Portland cement thelime content is about one-half. Furthermore, all components used in theactivation of blast-furnace slag according to the claimed method arecompounds of low calcium content, which means a calcium content below 3% by weight of the slag.

Furthermore, it was found that the reaction will be much more active ifa detergent is also added which reduces surface tension, disperses andprevents lump formation. Surface tension reducing agents are detergentssuch as complexed polyphosphates; nitrates such as dicyandiamide;alcoholates such as glycol and glycerine; oils; cellulose derivates andsulphates. The surface tension reducing agent is usually present in anamount of 0.1-2 % by weight of the slag. A phosphate having surfacetension reducing action such as sodium tripolyphosphate will act both asan acidic component and a surface reducing agent. MgO and phosphate perse do not react with slag and water, only in combination.

Sometimes it is advantageous to use a combination of MgO with otherearth metal oxides. Al₂ O₃ has positive effects similar to those of MgO,improves the reactivity of the slag and its resistance to chlorides.Titanium oxide imparts resistance to acidic actions, e.g. incontaminated air (sulfur deposition), and forms resistant crystals withsilica gels. ZrO₂ gives a reliable security against alkaline attack.

An example of a strongly acting sulfate is sodium bisulfate, NaHSO₄,which on account of its strongly acidic reaction is often usedindustrially instead of sulfuric acid.

The hitherto known activators mostly set too rapidly (in the case ofPortland cement too slowly), and no suitable control could be achieved.This is possible with the claimed method, either by addition of 0.1-2%by weight of surface-tension reducing agents or fluxing (plasticizing)agents, e.g. lignosulfonate, melamine, naphthalene-formaldehyde, sodiumgluconate or the like, or by plaster of Paris or anhydrite (about 3 %)or by using a mixture of different phosphates having different times ofreaction. Thus, it will be possible to obtain a binding agent which willharden within half an hour for prefabricated concrete elements, wherebymore precast units can be made per day, or it will be possible toincrease the setting time to about 2.5 hours which will be necessary forcasting on a building site.

By the addition of amorphous silicic acid, e.g. in the form of thefiltered residual product from electrometallurgical processes (such assilicon ferrosilicon or silicon chrome manufacture), having an SiO₂content between 75 and close to 100 % and usually a specific area of atleast 20 m^(2/) g, so called silica fume or silica, the compressivestrength and density can be further improved, preferably in combinationwith plasticizing agents.

The amorphous silicic acid is suitable used in an amount of 0.6 to 2 %weight, based on the dry concrete or 4 to 15 % by weight, based on theslag.

The new material is denser than concrete from Portland cement, isbrighter is color and lighter in weight. The new concrete can also beused as a plaster or porous or light-weight concrete, if a pore-formingagent or light-weight aggregate of the type of perlite, or vermiculiteor heat expanded porous clay pellets is added. The light-weightaggregate can be included in an amount of about 10-60% by weight,depending on the intended use of the concrete. Of course, it is possibleto mix the concrete with steel, glass, mineral or plastic fiberreinforcement in an amount of about 5 % by weight. A combination withbitumen (asphalt) is also possible.

The advantage of the improved slag concrete according to the presentinvention as compared to common concrete from Portland cement is aboveall a higher compressive and tensile strength, as seen from the tablebelow. This includes both a higher short-term strength which enablesremoval of moulds in building sites to be carried out after about 10hours for wall mouldings and after about 16 hours for vault mouldings,which results in great savings, and also an increasing strength forseveral months, while conventional concrete reaches maximum values afterabout 28 days.

The resistance to salt was tested at Chalmers Institute of Technology inGothenburg, Sweden for 4 months in a 30 % calcium chloride solution. Nodeterioration or cracking could be observed, as occurs in commonconcrete after a few weeks in highly concentrated calcium chloridesolution.

Protection against attack by rust is achieved in common concrete by thefree lime in the form of Ca(OH)₂ formed in the final stages of hydrationbeing deposited on the steel surfaces and protecting by its high pH thesteel from oxidation by penetration of water, oxygen or CO₂ from theair. However, calcium hydroxide is an unstable substance which isdissolved by water and converted by CO₂ (carbonatization). In the newconcrete, MgO which has a higher pH than lime forms the rust protection.Calcined MgO is resistant to water, oxygen and CO₂ and therefore morereliable than lime. In addition, the new concrete is much denser (lessporous) and therefore makes more resistance to penetrating water, oxygenor CO₂, which also results in an improved adherence to the steelreinforcement. The stability of the high pH value in the new concretewas also checked at Chalmers Institute of Technology by means of a bathof phenolphthalein which is a pH indicator. Permanent high pH is seenfrom unchanged red color which is not the case with Portland cementconcrete.

The combination of MgO and phosphate is hitherto known mostly from themanufacture of refractory ceramics but will also result in an improvedfire-resistance of the activated blast-furnace slag. Usual concrete doesnot withstand temperatures higher than about 500° C.

The reason for the sensitivity to high temperatures of Portland cementis substantially the presence of chemically bound water. The physicallybound water (capillary water) is removed at about 105° C. without anydeleterious action. The chemically bound water is released later, butwith cracking which will then result in decomposition. The unstable freelime Ca(OH)₂ will be converted into CaCO₃ and H₂ O, by CO₂ in the air.At the same time the liberated water will also attack the tri- anddicalcium silicates formed during hydration which will be converted intounstable calcium silicate hydrate. While concrete of Portland cementconsists of calcium-silica-hydrate, which leaches out by CO₂ in the air,in the new concrete an absolutely stablecalcium-silica-magnesia-alumina-hydrate is formed. In addition, thealpha phase of quartz (SiO₂) present in the concrete will be convertedinto a different crystal form with increase in volume, which will alsocontribute to cracking (see R.K. Iler "Chemistry of Silicates"). In thecombination of blast-furnace slag, phosphate and MgO there is no freelime and the SiO₂ of the granulated slag is amorphous, wherefore theserisks are not present. In uses where temperatures above 1000° C. canoccur, it may be suitable to replace the stone material of aggregateswhich may expand in heat, with refractory ceramic materials.This isrequired only in an exceptional case.

The new concrete may also be combined with bitumen (asphalt) in roadpavings.

As examples of the action of the new combination of activators withregard to compressive and tensile strengths, reference may be made tothe following test results obtained with a mixture of 100 weight percentof slag, 10 units of sodium tripolyphosphate, 7.5 weight percent of MgO,353 units of sand and 40 units of water.

    ______________________________________                                                   Compressive strength                                                                         Tensile strength                                    Age        MPa            MPa                                                 ______________________________________                                        1     day       6.2           1.2                                             3     days     26.0           3.7                                             7     days     40.9           6.3                                             28    days     81.3           10.4                                            ______________________________________                                    

These values are more advantageous than the corresponding values ofPortland cement (after 28 days 49.0 and 7.9 MPa, respectively). By theadditions mentioned above, the tabled values can be further improved.

As compared to Portland cement concrete the novel concrete achieves thefollowing advantages.

1. Higher mechanical resistance, i.e. higher compressive and tensilestrengths.

2. Higher chemical resistance.

3. No carbonatization, i.e. precipitation of unbound lime, which mayresult in deterioration of the concrete.

4. No salt attack. A road paving will not be damaged by road salt. Alonger life for concrete bridges A possibility of making resistantconcrete boats.

5. Not alkaline in spite of pH 12. No unbound lime, whereforereinforcement by glass fibres is possible. (If desired, a special typewith ZrO₂ may be manufactured).

6. Lighter than Portland cement concrete, structures may be madethinner.

7. The possibility of making thinner layers or thickness makes theconstruction cheaper, apart from the fact that slag is cheaper thanPortland cement.

8. Much denser.

9. Better adherence to steel and better protection against rusting ofthe steel adhered to the concrete.

10. Higher refractoriness (fire resistance).

11. Resistance to frost.

12 Facilitates casting in cold weather.

13. Better material than cement mortar for plastering, because of animproved adherence to concrete.

14. Lower requirements for moist hardening of freshly cast concrete

15. Similar to usual concrete, the new material may be rendered porousto obtain a light-weight concrete which has great advantages as comparedto traditional porous concrete and light-weight concrete, since the cellstructure is mechanically stronger and the new material is nothygroscopic.

16. Lighter color.

I claim:
 1. In a method of making a building material by activation oflatently hydraulic ground granulated amorphous basic blast-furnace slagto form a direct acting hydraulic binder, wherein the method comprisesmixing the slag, with water, sand, gravel, and an activator, said slag,water, sand, gravel and activator being present in amounts effective toenable the slag to react chemically with the water, in combination withthe sand and gravel, to produce a concrete of desired strength, theimprovement comprising forming the activator as a combination of anacidic component and a basic component, said acidic component being aphosphate or mixture of phosphates in an amount of 2 to 40% by weightbased on the amount of the slag, said phosphate or mixture of phosphateshaving surface tension reducing action or said method further comprisingadding a detergent or mixture of detergents to said slag, sand, gravel,and activator, said basic component being magnesium oxide, or magnesiumoxide in combination with aluminum oxide, titanium oxide, zirconiumoxide, or zinc oxide, said basic component being present in an amount of2 to 20% by weight based on the amount of the slag, said improvementcausing the formation of a concrete of great mechanical strength andhigh chemical resistance with the magnesium oxide and phosphate ormixture of phosphates incorporated into the concrete without the needfor heating at a high temperature.
 2. The method as in claim 1, whereinthe acidic component is sodium tripolyphosphate.
 3. The method as inclaim 1, further comprising adding plaster or Paris, anhydrite,plasticizing agents, or a combination thereof in an amount effective toalter the rate at which the concrete hardens.
 4. The method as in claim1, further comprising adding an amorphous silic acid in an amount of 4to 15% by weight of the slag.
 5. The method as in claim 1, furthercomprising adding a component selected from the group consisting ofsteel, glass, mineral, and plastic fiber in an amount sufficient toreinforce the concrete.
 6. The method as in claim 1, further comprisingadding material having a high porosity in an amount sufficient to form aconcrete suitable for use as porous concrete.
 7. The method as inn claim1, wherein the slag comprises 30-40% CaO, 35-40% SiO₂, 7-10% MgO, 10-20%Al₂ O₃, 0.5-2% Fe₂ O₃ +FeO, 1-2% K₂ O+Na₂ O and 0.5-3% SO₃.
 8. Themethod as in claim 1, wherein the building material has no unbound lime.9. The method, as in claim 1, wherein the activator further comprises anacidic sulfate, said phosphate or mixture of phosphates and said acidicsulfate together being present in an amount of 2 to 40% by weight basedon the slag.
 10. The method as inn claim 9, wherein the acidic sulfateis NaHSO₄.
 11. The method as in claim 1, wherein the basic component ismagnesium oxide in combination with aluminum oxide, titanium oxide orzirconium oxide.
 12. The method as in claim 11, wherein the basiccomponent is magnesium oxide in combination with titanium oxide orzirconium oxide.
 13. The method as in claim 1, wherein the basiccomponent is magnesium oxide.
 14. A method as in claim 1, wherein themixing of the slag, water, sand, gravel and activator causes a hydraulicreaction with the slag and wherein the improvement comprises includingas the phosphate or mixture of phosphates a phosphate having sufficientsurface tension reducing action to reduce surface tension amongreactants of said hydraulic reaction, to disperse said reactants and toprevent lump formation among said reactants.
 15. A method as claimed inclaim 1 wherein the mixing of the slag, water, sand, gravel andactivator causes a hydraulic reaction with the slag, wherein said methodincludes the addition of said detergent or mixture of detergents andwherein the improvement comprises mixing the slag, sand, gravel andactivator with said detergent or mixture of detergents in an amounteffective to reduce surface tension among reactants of said hydraulicreaction, to disperse said reactants and to prevent lump formation amongsaid reactants.
 16. A method as claimed in claim 3 wherein plaster ofParis or anhydrite is added in an amount of about 3% by weight based onthe slag.